Spring-loaded contour following end effectors for lapping/polishing

ABSTRACT

End effectors are provided for performing surface lapping using a robot. The end effectors allow orthogonal surface contact in order to maintain optimum pressure applied by the robot. One or more end effectors include a base, a plate, a lapping pad attached to the plate, and a pivot joint. The pivot joint allows the plate to pivot about two substantially orthogonal axes. The base is attached to an arm of a robot. The end effector includes a component for absorbing applied pressure, such as a spring-loaded shaft or a pneumatic shaft. In an aspect of the invention, the two axes are substantially parallel to the planar surface.

RELATED APPLICATION

[0001] This patent application is related to concurrently-filed patentapplications entitled “Contour Following End Effectors forLapping/Polishing”, bearing attorney docket number BOEI-1-1101, and“Automated Lapping System”, bearing attorney docket number BOEI-1-1121,which are hereby incorporated by reference.

GOVERNMENT LICENSE RIGHTS

[0002] This invention was made with Government support under U.S.Government contract F33615-97-2-3400 awarded by United States Air Force.The Government has certain rights in this invention.

FIELD OF THE INVENTION

[0003] This invention relates generally to lapping and polishingsurfaces and, more specifically, to robotic lapping and polishing.

BACKGROUND OF THE INVENTION

[0004] Injection-molded aircraft canopies and windshields offertremendous benefits to aircraft in cost, weight, and impact tolerance. Amajor cost in this manufacturing process is the injection mold itself.Surfaces of canopies and windshields are finished to a quality similarto an optic lens in order to prevent pilots from being subjected tovisual distortion. The precise optics for canopies and windshields arebuilt into the injection mold. The injection molds are lapped orpolished by hand, section by section, using a diamond plated lappingmaterial. Hand polishing or lapping an injection mold takes severalman-years to accomplish. Thus, lapping or polishing is very costly. Handpolishing or lapping also does not ensure that the precise, opticsurface finish quality has been met.

[0005] Therefore, there exists an unmet need to reduce the cost andincrease the accuracy of lapping or polishing.

SUMMARY OF THE INVENTION

[0006] The present invention provides end effectors for performingsurface lapping using a robot. The end effectors allow orthogonalsurface contact in order to maintain optimum pressure applied by therobot.

[0007] The present invention includes one or more end effectors with abase, a plate, a lapping pad attached to the plate, and a pivot joint.The pivot joint allows the plate to pivot about two substantiallyorthogonal axes. The base is attached to the robotic arm. The endeffector includes a component for absorbing applied pressure.

[0008] In an aspect of the invention, the component includes aspring-loaded shaft or a pneumatic shaft.

[0009] In another aspect of the invention, the two axes aresubstantially parallel to the planar surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The preferred and alternative embodiments of the presentinvention are described in detail below with reference to the followingdrawings.

[0011]FIG. 1 is a perspective view of an end effector in operation witha robot;

[0012]FIG. 2 is an exploded view of exemplary materials layered on anend effector;

[0013]FIGS. 3A and B illustrate a spring-loaded, universal joint endeffector;

[0014]FIGS. 4A and B illustrate a spring-loaded, hexagonal joint endeffector;

[0015]FIGS. 5A and B illustrate a gimbaled joint end effector with aspring-loaded shaft;

[0016]FIGS. 6A and 6B illustrate a half ball and socket joint endeffector with a spring-loaded shaft;

[0017]FIGS. 7A and 7B illustrate a pneumatic end effector; and

[0018] FIGS. 8A-C illustrate a multi-end effector support.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 shows an embodiment of an end effector 40 according to thepresent invention that is attached to a robot 42 for polishing andlapping a work product 44. A non-limiting example of the product 44 is acore or cavity injection mold for making polycarbonate aircraftcanopies. The work product 44 suitably entails a high degree ofpolishing or lapping accuracy. For example, precise optical propertiesfor injection molds must be attained in order to produce opticallyflawless or near-flawless polycarbonate molded canopies. In order toattain this desired level of accuracy, the end effector 40 pivots at anend of the robot 42, but does not rotate about an axis that isperpendicular to a planar surface of the end effector 40. In otherwords, the end effector 40 maintains a substantially orthogonal positionrelative to the work product 44.

[0020] The spring-loaded end effectors 40 are suitable for use with arobot that is configured with rigid motion and fixed positioning ascompared to robots configured with soft float functions, such as Fanucrobots. A non-limiting example of the robot 42 is a Cooper robot.Without soft float, shut-offs may occur if the robot 42 applies too muchpressure to a surface. The spring-loaded end effectors 40 allow therobot 42 to apply continuous, consistent pressure without incurringunnecessary shut-offs. The present invention far exceeds thecapabilities of a human operator, therefore lapping and polishingevolutions take a fraction of the time taken by a human operator. Thespring-loaded end effectors 40 include springs or pressureapplying/absorbing devices for absorbing a predefined amount of pressurein order to apply pressure-loaded diamond laps on the work surface foraccelerated material removal, and to avoid unnecessary robot shutdownsdue to over travel.

[0021] As shown in FIG. 2, the end effector 40 suitably includes alapping plate 50 with applied layers of materials that aid in lappingthe work product 44. In one embodiment, the layers of materials includeone or more silicon adhesive layers 54 interleaved with one or moresolid acrylic rings 56. A pitch substance 60, such as tree pitchproduced by Universal Photonics, Inc., Adolf Miller, or Zophar Mills,Inc., is applied to the last acrylic ring 56. A polishing or abrasivematerial 62, such as a diamond-plated lapping material, is attached tothe pitch 60. The robot 42 applies pressure to the work product 44through the end effector 40 in order to for the pitch 60 to conform tothe surface of the work product 44. The robot 42 moves the end effector40 over a section of the surface of the work product 44 that entails thesame curvature to which the pitch 60 conforms.

Spring-Loaded Joints

[0022]FIGS. 3A and B illustrate a non-limiting example end effector 100that suitably attaches to the robot 42 (FIG. 1). The end effector 100includes a universal joint 104 that couples a base mount 106 to alapping plate 110. The base mount 106 suitably attaches to the robot 42(FIG. 1). The universal joint 104 suitably includes a U-shaped receiverportion 114, a pin housing 116, and a U-shaped lapping plate portion120. The U-shaped receiver portion 114 is part of or is securelyattached to the base mount 106. The U-shaped lapping plate portion 120is suitably part of or is alternatively securely attached to, thelapping plate 110.

[0023] A first pin 124 is mounted through the U-shaped receiver portion114 and the pin housing 116. The pin housing 116 rotates about alongitudinal axis of the first pin 124. Second and third pins 130 and132 are mounted through the U-shaped lapping plate portion 120 and intothe pin housing 116 to allow the U-shaped lapping plate portion 120 torotate about a longitudinal axis of the second and third pins 130 and132. The second and third pins 130 and 132 are substantially axiallyorthogonal to the first pin 124. Thus, the universal joint 104 allowsthe lapping plate 110 to rotate about the axis of the first pin 124 andthe axis of the second and third pins 130 and 132 without allowingrotation of the lapping plate 110 itself.

[0024] A compression spring 140 encircles the universal joint 104,thereby putting expanding pressure on the base mount 106 and the lappingplate 110. When pressure is applied to the lapping plate 110, theU-shaped lapping plate portion 120 slides the second and third pins 130and 132 through the compression slots 144 while compressing thecompression spring 140.

[0025]FIGS. 4A and B illustrate a spring loaded, hexagonal ball andsocket joint end effector 200. The end effector 200 includes a base 204,a hexagonal ball 202, and a lapping plate 206 with a hexagonal bushing210. FIG. 4B is a cutaway view of the end effector 200. The hexagonalball 202 includes a first cavity 212 along the centerline of a shaft ofthe hexagonal ball 202 and a second cavity 214 within a portion of thebase 204. A single flexible retaining wire 216 is attached at opposingsides of the second cavity 214 by first and second clamp screws 218 and220. The flexible retaining wire 216 travels from the first clamp screw218 through the first cavity 212 and out of the hexagonal ball 202around a securing pin 222 back into the hexagonal ball 202 to the secondclamp screw 220. The securing pin 222 is securely attached within thehexagonal bushing 210. A compression spring 208 is wrapped around theshaft of the hexagonal ball 202 and applies an expanding force to thebase 204 and the hexagonal bushing 210.

[0026] When pressure is applied to the lapping plate 206, the spring 208compresses and the flexible retaining wire 216 flexes within the secondcavity 214. The flexible retaining wire 216 keeps the hexagonal ball 202within the hexagonal bushing 210.

Spring-Loaded Shafts

[0027]FIGS. 5A and B illustrate a gimbaled-joint end effector 150 with aspring-loaded shaft. The gimbaled-joint end effector 150 includes agimbaled-joint section 156 coupled to a spring-loaded shaft section 158.The spring-loaded shaft section 158 includes a first base 162, a secondbase 164, first and second shaft bushings 170 and 172, a spline shaft176, and a spring 178. The second base 164 is securely attached to abase of the gimbaled-joint section 156. The second base 164 includes acavity for receiving the second shaft bushing 172. The second shaftbushing 172 includes a cavity with a toothed wall configured to receivethe spline shaft 176. The spline shaft 176 and the second shaft bushing172 are suitably secured within the second base 164 by a pin 180 thatpasses through opposing sidewalls of the second base 164, the secondshaft bushing 172, and the spline shaft 176. The first shaft bushing 170is positioned within a cavity of the first base 162. The first shaftbushing 170 includes a cavity with toothed walls for receiving thespline shaft 176. The first shaft bushing 170 includes a vertical notch186 for receiving a pin 182 that is securely attached to the splineshaft 176. The vertical notch 186 allows for motion of the spline shaft176 vertically within the first shaft bushing 170.

[0028] A spring 178 is positioned around the spline shaft 176 betweenthe first and second shaft bushings 170 and 172. The spring 178maintains an expanding force on the first shaft bushing 170 and thesecond shaft bushing 172. Thus, when pressure is applied to thegimbaled-joint section 156, the second shaft bushing 172 moves thespline shaft 176 with the attached pin 182 up the vertical notch 186 andcompresses the spring 178.

[0029]FIGS. 6A and B illustrate a one-half ball socket end effector 240with spring-loaded shaft. The one-half ball and socket end effector 240includes a socket housing 244, a half-ball lapping plate 246, and firstand second pins 248 and 250. The lapping plate 246 includes a one-halfball joint portion 256 that is pivotally received by a semi-circularcavity 252 formed by the socket housing 244. The pins 248 and 250 passthrough opposite sides of the socket housing 244 and protrude into thecavity 252. The distance between the pins 248 and 250 is less than adiameter of a widest part of the one-half ball joint portion 256. Thus,the one-half ball joint portion 256 swivels within the socket housing244 and is maintained within the cavity 252 by the pins 248 and 250.

[0030] The socket housing 244 is coupled to a shaft 260 that is suitablycoupled to a robot arm. The shaft 260 receives a spring support washer262 and a compression spring 264. A securing pin 266 allows the shaft260 to be slidably received by a support structure (not shown). Whenpressure is applied to the half-ball lapping plate 246, the shaft 260slides through the support structure and compresses the spring 264between the spring support washer 262 and the support structure.Therefore, the one-half ball socket end effector 240 absorbs someapplied pressure in order to avoid any unnecessary robot shut-offs.

Pneumatic Shock

[0031] FIGS. 7A-C illustrate a one-half ball socket end effector 300with a pneumatic shock. The end effector 300 includes a pneumatic shocksection 304 that connects to a end effector portion 306. The pneumaticshock section 304 includes a pneumatic housing 310, a shock 312, ahousing cap 314, and a connector 316 coupled to a pneumatic input line320. The pneumatic input line 320 receives pressurized air from apneumatic source pump (not shown) that is controlled by a controllingdevice (not shown). The shock 312 includes a shaft 324 that passesthrough an opening at a first end of the pneumatic housing 310. Theshock 312 also includes a plunger portion 326 attached to the shaft 324.The plunger portion 326 is larger in diameter than the shaft 324 andlarger than an opening at a first end of the pneumatic housing 310. Theplunger portion 326 is surrounded by a seal 328 that mates with aninterior wall of the pneumatic housing 310 for avoiding air leakage passthe plunger portion 326. A second end of the pneumatic housing 310 thatis opposite the first end is capped by the housing cap 314 that includesa receiving cavity for securely connecting to the connector 316. Theconnector 316 securely receives the pneumatic input line 320 from thepneumatic source (not shown).

[0032] The lapping plate portion 306 includes a lapping plate housing330, a lapping plate cap 334, a lapping plate 336, and a pressure sensor338. The lapping plate housing 330 includes a first cavity for threadilyattaching the housing 330 to the shaft 324 of the shock 312. The lappingplate housing 330 includes a second cavity 340 that is sized to receivethe lapping plate cap 334 and the lapping plate 336. The lapping plate336 is suitably a half ball that is attached to the lapping plate cap334. When the half ball and lapping plate cap 334 are inserted into thesecond cavity 340, cross-pins 344 are inserted along a cord of theswivel plate base 330 near the opening of the second cavity 340. Thecross-pins 344 are separated at a distance that is less than thediameter of the half ball, thereby keeping the half ball within thesecond cavity 340. The pressure sensor 338 is mounted at one end of thesecond cavity 340 opposite the opening of the cavity 340. The pressuresensor 338 is attached to the controller device (not shown). Thepressure sensor 338 senses pressure from the lapping plate cap 334 basedupon pressure on the lapping plate 336 causing the lapping plate cap 334to move within the cavity 340. The controller device instructs increasesor decreases in pneumatic pressure within the pneumatic housing 310based on the sensed applied load pressure compared to the prescribedpressure.

Multiple Unit

[0033] FIGS. 8A-C illustrate a multi-end effector support 350. Thesupport 350 includes a plurality of arms 356 that extend radially from acenter shaft 360. The center shaft 360 is attached to a base (not shown)that is coupled to the robot 42 (FIG. 1). The types of end effectorunits that can be used with the multi-end effector support 350 are anyone of the ones shown in FIGS. 3-7. In order to accommodate theplurality of arms 356, multiple size lapping plates are interspersed andattached to the ends of each of the spring-loaded end effector units 240attached to the arms.

[0034] It will be appreciated that various jointed end effectors can beused at the end of any of the spring-loaded shafts or at the end of thepneumatic shock. An example end effector that can be used is across-pinned ball socket joint end effector that is described in therelated copending U.S. Patent Application identified above andincorporated by reference.

[0035] While the preferred embodiment of the invention has beenillustrated and described, as noted above, many changes can be madewithout departing from the spirit and scope of the invention.Accordingly, the scope of the invention is not limited by the disclosureof the preferred embodiment. Instead, the invention should be determinedentirely by reference to the claims that follow.

What is claimed is:
 1. A robotic system for lapping a surface, therobotic system comprising: a robotic arm for applying pressure; and aend effector unit including: a base attached to the robotic arm; aplate; a lapping pad attached to the plate; a pivot joint for allowingthe plate to pivot about two orthogonal axes; and a component forabsorbing pressure applied to the end effector unit.
 2. The system ofclaim 1, wherein the component includes a spring-loaded shaft.
 3. Thesystem of claim 1, wherein the component includes a pneumatic shaft. 4.The system of claim 3, wherein the component further includes apneumatic sensor for sensing pressure applied to the plate.
 5. Thesystem of claim 1, wherein the two axes are substantially parallel tothe planar surface.
 6. The system of claim 5, wherein the two axes aresubstantially orthogonal to a direction of the pressure applied to therobot.
 7. The system of claim 5, wherein the pivot joint includes auniversal joint.
 8. The system of claim 5, wherein the pivot jointincludes a gimbaled joint.
 9. The system of claim 5, wherein the pivotjoint includes a needle bearing joint.
 10. The system of claim 5,wherein the pivot joint includes a ball and socket joint.
 11. The systemof claim 10, wherein the ball and socket joint includes a half-ball andsocket joint.
 12. The system of claim 10, wherein the ball and socketjoint includes a crossed-pin ball and socket joint.
 13. A lapping endeffector comprising: a base; a plate having a planar surface; a lappingpad attachable to the planar surface of the plate; and a pivot joint forallowing the plate to pivot about two axes, the pivot joint including apressure absorbing component for absorbing a predetermined amount ofpressure applied to the plate.
 14. The system of claim 13, wherein thepressure absorbing component includes a spring.
 15. The system of claim13, wherein the two axes are substantially parallel to the planarsurface.
 16. The system of claim 15, wherein the pivot joint includes auniversal joint.
 17. The system of claim 15, wherein the pivot jointincludes a hexagonal ball joint.
 18. The system of claim 15, wherein thepivot joint includes a crossed-pin ball and socket joint.
 19. A roboticsystem for lapping a surface, the robotic system comprising: a roboticarm; a support member coupled to the robotic arm; and a plurality of endeffector units including: a base attached to the support member; a platehaving a planar surface; a lapping pad attachable to the planar surfaceof the plate; and a pivot joint for allowing the plate to pivot abouttwo axes; and one or more components for absorbing pressure applied toeach end effector unit.
 20. The system of claim 19, wherein the one ormore components include a spring-loaded shaft.
 21. The system of claim19, wherein the one or more components include a pneumatic shaft. 22.The system of claim 19, wherein the one or more components include aspring.
 23. A method for lapping a surface, the method comprising:applying pressure by a robot between a lapping pad attached to a platehaving a planar surface and the surface; pivoting the plate to moveabout two axes, wherein the two axes are substantially parallel to theplanar surface and the applied pressure is substantially orthogonal tothe two axes; and absorbing at least some of the applied pressure.